This invention relates to a Stirling cycle engine in which heat from an external source is converted to useful mechanical energy. More particularly, the present invention relates to an improved arrangement of the heater, regenerator and cooler elements of the engine to provide an engine which is more compact without any loss of operating efficiency.
Stirling cycle engines are well-known in the prior art. A conventional Stirling cycle machine operates on a regenerative thermodynamic cycle, with cyclic compression and expansion of the working fluid at different temperature levels. The fluid flow is controlled by volume changes which create a set conversion of heat to work or vice versa. In a typical stirling engine, operating as a prime mover, heat is supplied to the working fluid when the fluid is in a "hot" or expansion chamber. Part of the heat is converted to work when, due to the absorbed heat, the working fluid, expands and thereby pushes on a piston which is coupled to a crank shaft that impart rotary motion. The working fluid is then displaced by a displacer through the regenerator, where most of the heat is drawn off. The working fluid is then forced into a "cold" or compression chamber, which is at some lower temperature. The piston then compresses the working fluid at the lower temperature. Thereafter, the working fluid is forced out of the cold chamber by a displacer, through the regenerator and into the hot chamber. As it passes through the regenerator the working fluid reabsorbs some of the heat previously deposited there. In the hot chamber, the working fluid again absorbs heat and the cycle of operation repeat itself. Therefore, the crank shaft is rotated due to the reciprocating motion of the displacer.
U.S. Pat. No. 4,578,949 issued to Takei et al, discloses one embodiment of a compact Stirling cycle machine. FIG. 1 is a cross sectional view of a prior art embodiment of a Stirling cycle engine 1. Engine 1 includes a displacer piston 2 and a power piston 3 operating within a cylinder 4. Cylinder 4 is divided into an upper expansion chamber 4a and a lower compression chamber 4b by displacer piston 2 and power piston 3. The upper chamber 4a and lower chamber 4b are connected with one another through a heater 5, regenerator 7 and cooler 6. The working fluid thereby can flow into the lower chamber 4b from the upper chamber 4a or vice versa. Heater 5, which receives heat from heat sources and communicates with upper chamber 4a of cylinder 4, projects radially from the top portion of cylinder 4 to extend over the heat source. Cooler 6, which communicates with lower chamber 4b of cylinder 4, projects radially from the lower portion of the cylinder 4 on the opposite side from which heater 5 extends. Therefore, the function of cooler 6 is not affected by the heat source, which results in a more efficient operation. However, this typical construction results in the engine having a large radial size, defined by the length of both heater 5 and cooler 6.